The present invention generally relates to the monitoring for alpha particle contamination and, more specifically, to the monitoring of alpha contamination without the use of a fan to draw air containing ions into the detector.
In any area where radioactive materials are handled, it is imperative, both for the protection of personnel and to avoid contamination of the environment, to continuously monitor personnel, equipment and clothing to prevent the release of radioactive contamination. Alpha contaminants, such as plutonium, are particularly difficult to detect because of the limited penetration of alpha particles in air. Alpha particles from typical contaminants travel no more than one inch in air. It is because of this characteristic that prior alpha detectors have been useful only when used in close proximity to the point of possible emission. Prior to the development of the long range alpha detector technology, alpha contamination could not be detected if it originated in a space that was too small for insertion of a conventional monitor. Prior detectors have normally been employed in personnel screening when moved slowly in close proximity to a person's body. Workers in nuclear processing facilities must place their hands and feet on sensors when moving from room to room. All of this can slow operations, as it is not currently possible to adequately screen personnel within a reasonable period of time.
It is also extremely difficult to monitor equipment for alpha contamination, again due to the limited range of alpha particles in air. Because of the monitoring difficulty, equipment that has been used in a potentially contaminated area is often classified as potentially contaminated and its further use is restricted to other controlled areas. If such equipment could be effectively monitored for contamination, the equipment could be released for use in uncontrolled areas. Previously, contamination inside assemblies has been impossible to detect without dismantling the assembly. The present invention allow contamination detection in any area that air can penetrate.
As used herein, the terms "long range," or "long distance" when referring to the detection capabilities of the present invention, shall mean detection from a range or distance of more than one (1) inch from the source of alpha radiation.
In the past, several instrument designs have been utilized to detect alpha radiation. Among these are GM tubes, ionization chambers, count rate detectors, and scintillation or gas flow proportional probes. While these instruments are capable of detecting alpha particles, they do so by directly detecting incident radiation, and must be within an inch of the source of the radiation. Also, these conventional alpha particle detectors can only scan an area approximately equal to the size of the detector.
The primary reason for an alpha particle's short flight path in air is its collision with air molecules. In almost all of these collisions, air ions are created which will have a longer life and area of influence than the alpha particles that created them. These are the ions that are detected by the present invention. The fact that the air ions have a longer range than the alpha particles relieves the necessity for having a detector moved over a person or equipment in order to detect the presence of alpha radiation.
Recently, several patent applications have been filed concerning new apparati for the detection of alpha detection from a long range. These include three applications concerning different embodiments of the long range alpha detector. The first application is Ser. No. 709,566, filed Jun. 3, 1991, for a Long Range Alpha Particle Detector, now issued as U.S. Pat. No. 5,184,019, dated Feb. 2, 1993. The second is Ser. No. 773,002, filed Oct. 8, 1991, for Single and Double Grid Long Range Alpha Detectors, now issued as U.S. Pat. No. 5,194,737, dated Mar. 16, 1993. The third is Ser. No. 799,464, filed Nov. 27, 1991, for Alternating Current Long Range Alpha Particle Detectors, now issued as U.S. Pat. No. 5,187,370, dated Feb. 16, 1993. Two additional applications have been filed concerning applications of the long range alpha detector. One is Ser. No. 864,747, filed Apr. 7, 1992, with the title Alpha Contamination Monitoring of Equipment Interiors now abandoned. The other is Ser. No. 864,746, filed Apr. 7, 1992, with the title of Radon Detector, which has received a Notice of Allowance dated May 11, 1993. The principle underlying each of these co-pending applications is that alpha particles, although themselves of very short range, create air ions which have a longer range and can be detected with the apparatus disclosed. As opposed to the present invention, these applications all involve use of a fan to draw air containing ions created by collision with alpha particles into the detector. The present invention uses no fan, but draws ions to the detector with electric fields. This overcomes the possible problem of stirring up dust and potential contamination and distributing it into the surrounding atmosphere, as with the detectors using fans to draw air into the detector.
The fact that long range alpha detectors, as described in the above-referenced applications, can detect alpha radiation at a considerable distance from its point of emanation allows for monitoring of contamination in several areas which are extremely difficult or even impossible for current detectors. The current invention accomplishes this by the use of electric fields to draw ions from remote and inaccessible locations into the detector.
It is another object of the present invention to provide apparatus for the detection of alpha radiation originating from inaccessible or other difficult to monitor locations.
It is therefore an object of the present invention to provide apparatus for the long range detection of alpha radiation without the need for air moving means to draw air containing ions created by collision with alpha particles into the detector.
Additional objects, advantages and novel features of the invention will be set forth in part in the description which follows, and in part will become apparent to those skilled in the art upon examination of the following or may be learned by practice of the invention. The objects and advantages of the invention may be realized and attained by means of the instrumentalities and combinations particularly pointed out in the appended claims.